Hello adibou,
The UPnP service works the same way. Applications / devices are automatically activated by UPnP service for the firewall and the correct ports are unlocked.
If you do not want this service, disable the UPnP service on your device (not the modem). Then your device will no longer send anything to your modem.
Regarding your question, the rule should no longer be present after the reboot. If you turn UPnP back on on your modem, the rule will be added back.
Greetings
Daniele